Origin, name and written symbols

The Sanskrit name for the syllable is praṇava, from a root nu "to shout, sound, praise", verbal pra-nu- being attested as "to make a humming or droning sound" in the Brahmanas, and taking the specific meaning of "to utter the syllable om" in the Chandogya Upanishad and the Shrauta Sutras. More rarely used terms are akṣara or ekākṣara, and in later times omkāra becomes prevalent.

A popular depiction of the Aum syllable in the Devanagari script () is a ligature of ओ+ँ (oṃ, encoded in Unicode at U+0950 ॐ, the Tibetan script variant ༀ at U+0F00, and the Chinese 唵 at U+5535 or 吽 at U+543D).

The syllable Aum is first described as all-encompassing mystical entity in the Upanishads. Today, in all Hindu art and all over India and Nepal, 'Aum' can be seen virtually everywhere, a common sign for Hinduism and its philosophy and mythology.

Upanishads and Sutra literature

The syllable is mentioned in all the Upanishads, specially elaborated upon in the Taittiriya, Chandogya and Mandukya Upanishad set forth as the object of profound religious meditation, the highest spiritual efficacy being attributed not only to the whole word but also to the three sounds a (a-kāra), u (u-kāra), m (ma-kāra), of which it consists.

In the following sutra it emphasizes, "The repetition of Om should be made with an understanding of its meaning". [2]

Puranic Hinduism

In Puranic Hinduism, Aum is the mystic name for the Hindu Trimurti, and represents the union of the three gods, viz. a for Brahma, u for Vishnu and m for Mahadev which is another name of Shiva. The three sounds also symbolise the three Vedas (Rigveda, Samaveda, Yajurveda).

According to Hindu philosophy(see Mandukya Upanishad), the letter A represents creation, when all existence issued forth from Brahma's golden nucleus; the letter U refers to Vishnu the god of the middle who preserves this world by balancing Brahma on a lotus above himself, and the letter M symbolizes the final part of the cycle of existence, when Vishnu falls asleep and Shiva has to breathe in so that all existing things have to disintegrate and are reduced to their essence to him. More broadly, Aum is said to be the primordial sound that was present at the creation of the universe. It is said to be the original sound that contains all other sounds, all words, all languages and all mantras.

Dvaita

VaishnavaDvaita philosophies teach that 'Aum' is an impersonal sound representation of Vishnu/Krishna while Hari Nama is the personal sound representation. A represents Krishna, U Srimati Radharani and M jivas. According to Sridhara Svami the pranava has five parts: A, U, M, the nasal bindu and the reverberation (nada). Liberated souls meditate on the Lord at the end of that reverberation. For both Hindus and Buddhists this syllable is sacred and so laden with spiritual energy that it may only be pronounced with complete concentration.

Advaita

In Advaita philosophy it is frequently used to represent three subsumed into one, a common theme in Hinduism. It implies that our current existence is mithyā and maya, "falsehood", that in order to know the full truth we must comprehend beyond the body and intellect the true nature of infinity. Essentially, upon moksha (mukti, samadhi) one is able not only to see or know existence for what it is, but to become it. When one gains true knowledge, there is no split between knower and known: one becomes knowledge/consciousness itself. In essence, Aum is the signifier of the ultimate truth that all is one.

In proper names

When Aum is a part of a place name (for example Omkareshwar), or is used as a man's name, it is spelled phonetically using ordinary letters of whatever Indian alphabet is used in the area. The adherents of Arya Samaj always use the ordinary letters अ, ऊ and म to write Aum.

With Buddhism's evolution and breaking away from Vedic/Hindu tradition, Aum and other symbology/cosmology/philosophies are shared with the Hindu tradition. This character often appeared as "唵" in Buddhist scripts in East Asia.